The present invention pertains to a system and method for monitoring the characteristics of rods comprising multiple segments. More particularly, the present invention relates to a system and method for monitoring the characteristics of cigarette filter rods having multiple segments and for ensuring that the rods are cut at desired locations along their lengths.
A typical cigarette comprises a wrapped tobacco column that optionally is tipped with a filter rod. The filter rod, in turn, may comprise plural segments. For instance, the filter rod may include a cellulose acetate (CA) segment adjacent to a cellulose acetate (CA) charcoal impregnated segment. Other known filter rods include an "air gap" disposed in the filter rod. As the name suggests, an air gap is a column of air disposed between filter segments.
The filter rods may be produced separately from the tobacco column, and later joined to the tobacco column in a tipping machine. More specifically, it is known to produce composite filter rods containing multiple filter rods, each filter rod constituting a separate filter rod which is subsequently combined with a tobacco column. For instance, FIG. 1 shows a composite rod made of alternating segments of cellulose acetate (i.e., segments 102, 106) and segments containing charcoal (i.e., segments 100, 104, 108). A total of four filter rods can be produced by cutting this composite rod into four equal length filter rods. Another known type of composite rod is shown in FIG. 2. This composite filter rod includes cellulose acetate segments (202, 206, 210, 214) and charcoal segments (200, 208 and 216). This composite filter rod also includes air gaps (204, 212) interposed between cellulose acetate segments (i.e., between segments 202 and 206, and between segments 210 and 214, respectively). This composite filter rod also produces four individual filter rods.
In the following discussion, the term "filter rod" is used to designate either a composite rod having multiple individual filter rods or to designate individual filter rods (depending on the context in which this term is used). The term "segment" is used to denote sections which are disposed within (or which will be disposed within) a filter rod. A segment of cellulose acetate (CA) which is impregnated with carbon is referred to alternatively as a "charcoal segment" for brevity.
FIG. 3 shows a machine 300 capable of producing the type of filter rod configuration shown in FIG. 2, which is described in U.S. Pat. No. 4,238,994 to Koch (which is incorporated herein in its entirety by reference). The machine 300 comprises two magazines or hoppers 302 and 304. Magazine 302 can hold rods made of acetate material and magazine 304 can hold charcoal impregnated CA rods. Rods from these two hoppers are transported by a series of conveyers 306 in a known manner to a combining conveyer 308. Before reaching conveyer 308, the rods may be cut into segments by rotary disk-shaped knives. At the combining conveyer 308, the segments are arranged into groups (e.g., group 310) comprising, for instance, the grouping pattern shown in FIG. 2. The spacing between adjacent groups forms the gaps in the filter rod.
Combining conveyer 308 transfers the groups of segments to the upper side of a running web 312. The web 312 contains an adhesive applied to its upper side by paster 314. The adhesive ensures that the segments in the groups maintain their axial relationship with respect to each other as they advance along the web 312 from the combining conveyer 308. The draping mechanism 316 next drapes the web 312 around the groups so that the web 312 is converted into a tubular envelope or wrapper. A seam on the web 312 is heated or cohered by a sealer 318. Thereafter, the web 312 is severed at regular intervals by a cutting mechanism 320 to yield filter rods of multiple unit length. The filter rods can then be transported to a filter tipping machine (not shown) via belt conveyor 324.
The length of the segments and the spacing between the segments should satisfy predetermined criteria. To this end, the machine 300 employs an optical detector 326. The optical detector 326 is positioned "upstream" from the cutting mechanism 320. The detector 326 transmits a beam of light through the advancing filter rod and detects the light after it passes through the rod. Light more readily passes through the gap segments than the cellulose acetate segments and the charcoal segments. Further, light more readily passes through the cellulose acetate segments than the charcoal segments. Hence, the output of the detector 326 can be used to determine the transition from one segment to another by noting changes in the output of the detector 326.
The machine 300 also employs an electrical encoder (not shown) associated with the cutting mechanism 320. The encoder outputs a pulse when the cutting mechanism severs a rod, and also outputs a series of pulses between each cut. The frequency of the pulses output by the encoder reflects the operating speed of the cutting mechanism 320 and also the speed at which the rods are advanced through the cutting mechanism 320. This encoder information is fed to circuit 327, along with the output of the detector 326. Together, the output of the detector 326 and the output of the encoder allow the circuit 327 to calculate the length of segments within the filter rod and also to determine whether the rods are being cut at desired locations. This information can also be used to reject faulty rods and to adjust the operation of the machine. More specifically, circuit 327 feeds control signals to a servomotor 328 which changes the speed of the transmission 330. These adjustments alter the location at which the cut is made.
Koch also discusses one type of logic circuit which can serve as the above-discussed circuit 327. Koch's circuit includes a plurality of counters which count pulses received from the encoder of the cutting mechanism 320. The counters begin counting when the detector detects a transition from one segment to an adjacent segment as the rod passes the detector 326. The length of the segments (and the location of the cut) can be gauged from the counts stored by the counters.
The above-described technique may have a number of shortcomings. It may not always be possible to uniformly detect the transition between filter rod segments. For instance, the output of the detector 326 may have a certain amount of noise. Further, the filter rod itself can have a number of anomalies, such as small unintended air gaps between filter segments (referred to as "air rings"). Factors such as these can complicate the detection of the transition between adjacent segments, thus potentially producing inaccurate length measurements when the segment transitions are detected by simply passing a stream of data points through a threshold detector in the real-time manner described in the Koch patent.
Further, as described above, different cigarettes may use a different sequence of filter segments. Koch's logic circuit comprises a combination of discrete logic units which may not be suitable for inspecting different types of filter rods without significant re-engineering of the circuit design.